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public void ReadFromFile (string textFile)
// Reads a text file (in fact a DXF file)
// for importing an Autocad drawing.
{
    string line1, line2;
    //these line1 and line2 is used for 
    //getting the a/m data groups...

    line1 = "0"; //line1 and line2 are are initialized here...
    line2 = "0";
    long position = 0;

    theSourceFile = new FileInfo (textFile); //the sourceFile is set.
    StreamReader reader = null; //a reader is prepared...

    try
    {
        reader = theSourceFile.OpenText();
        //the reader is set ...
    }

    catch (FileNotFoundException e)
    {
        MessageBox.Show(e.FileName.ToString() + " cannot be found");
    }

    catch
    {
        MessageBox.Show("An error occured while opening the DXF file");
        return;
    }

    /////////////////////////////////////////
    //This part interpretes the drawing objects
    //found in the DXF file...
    /////////////////////////////////////////

    do
    {
        if (line1 == "0" && line2 == "LINE")
            LineModule(reader);
        else if (line1 == "0" && line2 == "LWPOLYLINE")
            PolylineModule(reader);
        else if (line1 == "0" && line2 == "CIRCLE")
            CircleModule(reader);
        else if (line1 == "0" && line2 == "ARC")
            ArcModule(reader);
 
        GetLineCouple (reader, out line1, out line2);
        //the related method is called 
        //for iterating through the text file 
        //and assigning values to line1 and line2...
    }
    while (line2 != "EOF");

    /////////////////////////////////////
    /////////////////////////////////////
 
    reader.DiscardBufferedData(); //reader is cleared...
    theSourceFile = null;
    reader.Close(); //...and closed.
}

Let me explain a little bit about the structure of a DXF file. In DXF files (they can be opened in Notepad) the data is stored in two-line (bi-line, dual, coupling..what ever you call it) structures. The first line contains a kind of an identifier (or a Tag) and the second line contains the data value. So in order to interpret a dxf file we must interperet lines two-by-two.

Depending on this dual structure we can interpret all entities that reside in a DXF file. But currently only LINE, LWPOLYLINE, CIRCLE and ARC entities can be recognizable. For near future I'm planning to add BSPLINE.

I provided plenty of comments in the source code, so please look in the source code itself for explanation of the modules.

DXF Viewer

Viewer part contains much more coding than the reader. As I mentioned above currently I can draw a limited number of shapes. I hope to expand it in near future.

While I'm developing the Viewer I got lot's of ideas and knowledge from the ucancode. It varies from double buffering techniques to making a GradientBackground.

In the beginning I said that the viewer is a MDI application. In this way you can open multiple DXF files to view. After opening a file, if you click on the "Window" button in the main menu you can see a list of the opened windows.

To make this add a menu item to the main menu, and then in its properties find MdiList and change its value to "true".

I made the gradient background with overriding OnPaintBackground event:

protected override void 
         OnPaintBackground(System.Windows.Forms.PaintEventArgs e)
//all drawing is made here in OnPaintBackground...
{
    base.OnPaintBackground(e);
    //you must pass "e" to the base method

    ...
    
    Graphics g = e.Graphics;
    Rectangle rect = new Rectangle(this.pictureBox1.Location, 
                         this.pictureBox1.Size);
    //In fact the pictureBox1 is hidden,
    // the sole purpose of it is 
    //to get its dimensions for defining the drawing area.

    System.Drawing.Drawing2D.LinearGradientBrush brush = 
        new System.Drawing.Drawing2D.LinearGradientBrush(
        rect, Color.SteelBlue, Color.Black, 
        System.Drawing.Drawing2D.LinearGradientMode.ForwardDiagonal);
 
    if (this.WindowState != FormWindowState.Minimized)
    {
        e.Graphics.FillRectangle(brush, rect);
        //gradient background

        Draw(g); //All drawing is made here...
    }

    brush.Dispose();

}

Conclusion

The main purpose of this project is to demonstrate that the dxf files can be read with the above mentioned techniques. In fact, the viewer part has a secondary priority at the beginning. Later on I paid some attention to it, but I cannot claim that the viewer is composed of the best practices.

The compressed file for the demo application the executable file and two sample dxf files. One of the dxf files is the one that can be seen in the screenshot. The drawing seems to be 3-D but it is not. it is drawn in 2D...